Reflection-type liquid crystal display device and fabrication process thereof

ABSTRACT

A reflection-type liquid crystal display device includes a first substrate, a second substrate facing the first substrate and carrying projections and depressions, a reflective electrode on the second substrate so as to cover the projections and depressions and in electrical contact with a switching device provided on the second substrate via a contact hole, and a negative liquid crystal layer between the first and second substrates, wherein the contact hole is disposed centrally to the reflection electrode and a structure controlling alignment of liquid crystal molecules in the liquid crystal layer is disposed so as to overlap the contact hole viewed in a direction perpendicular to the second substrate.

This is a divisional of Ser. No. 10/754,417, filed Jan. 9, 2004 now U.S.Pat. No. 7,072,014, which is a divisional of Ser. No. 10/316,659, filedDec. 11, 2002, which is now U.S. Pat. No. 6,897,924, issued on May 24,2005.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on Japanese priority application No.2001-377791 filed on Dec. 11, 2001, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to reflection-type liquidcrystal display devices used in a low-power apparatuses such as portableterminals.

A reflection-type liquid crystal display device is a liquid crystaldisplay device that achieves display of images by incorporatingenvironmental light such as interior illumination light or sunlight andcausing the same to reflect toward an observer by means of a reflector.

Because of the operational principle, the reflection-type liquid crystaldisplay device does not need a backlight and has an advantageous featureof low power consumption. Thus, reflection-type liquid crystal displaydevices are used extensively for portable terminals.

In order to achieve bright and clear representation of images in areflection-type liquid crystal display device, it is necessary to designthe liquid crystal display device such that as much environmental lightas possible is incorporated and reflected toward the observer in thewhite representation mode and that the reflection of the incorporatedlight toward the observer is suppressed as much as possible in the blackrepresentation mode.

Thus, there is a proposal of a reflection-type liquid crystal displaydevice that uses a phase-change type guest-host (GH) mode (D. L. Whiteand G. N. Taylor, J. Appl. Phys. 45, pp. 4718, 1974). Because a GH-modereflection-type liquid crystal display device does not require apolarizer, there is a distinct advantage in such a GH-modereflection-type liquid crystal display device that a brightrepresentation is achieved in the white representation mode.

On the other hand, a GH-mode liquid crystal display device has adrawback in that a bright representation is obtained also in the backrepresentation mode and the contrast ratio is limited to the range of5-6.

Meanwhile, there is a proposal of a reflection-type liquid crystaldisplay device of a twisted nematic mode that uses a single polarizer asin the Japanese Laid-Open Patent Publication 6-11711.

This conventional reflection-type liquid crystal display device isbasically a horizontally oriented liquid crystal device in which liquidcrystals having a positive dielectric anisotropy are twisted. In theforegoing conventional reflection-type liquid crystal display device,the incoming environmental light is converted to a linear polarizationlight by a polarizer, and the linearly polarized light thus obtained ispassed through a liquid crystal layer or a phase compensation filmhaving a ¼-wavelength retardation, so that there is achieved a 90 degreeangle of polarization plane between the incident light passed throughthe polarizer and the reflection light returning to the polarizer.

Thus, in this conventional liquid crystal display device, the blackrepresentation is achieved by absorbing the rotated reflection light bythe polarizer. Because of the use of the polarizer, the foregoingconventional liquid crystal display device can provide only about 40% ofbrightness in the while representation mode as compared with the case ofthe GH-mode liquid crystal display device. However, the liquid crystaldisplay device can achieve a contrast ratio of 12-14 in view ofefficient absorption of the light in the black representation mode.

Further, there is a proposal of improving the contrast ratio in aTN-mode liquid crystal display device by way of compensating for theblack representation, by reducing the amount of retardation of the phasecompensation film by the magnitude of the residual retardation of theliquid crystal layer. See Japanese Laid-Open Patent Publication11-311784. With this, the contrast ratio is improved to about 16-18.

In a reflection-type liquid crystal display device, the visibility ofrepresentation is defined by brightness and contrast ratio. Thus, a highvisibility is achieved even in the case of low contrast ratio when therepresentation is bright. When the representation is dark, on the otherhand, a large contrast ratio is required. See The Journal of theInstitute of Television Engineers of Japan, Vol. 50, No. 8, pp.1091-1095 (1996).

A contrast ratio of about 12 is needed in order to realize thevisibility comparable to that of a GH-mode liquid crystal display deviceby using a liquid crystal display device having a single polarizer, thelatter liquid crystal display device can provide the brightness of only40% of the brightness of a GH-mode liquid crystal display device. Byusing the technology noted in the above reference, it becomes possibleto achieve a contrast ratio of 16-18 by using a T-N mode liquid crystaldisplay device.

Because of the foregoing reason, and further in view of betterreliability, a TN-mode liquid crystal display device having a singlepolarizer is used widely in these days for a reflection-type liquidcrystal display device.

In a TN-mode liquid crystal display device having a single polarizer, itshould be noted that the upper and lower substrates are subjected torubbing processing in different directions so as to realize the twistedstructure in the liquid crystal layer. As a consequence, the anchoringdirection of the liquid crystal layer is not coincident in the upper andlower substrates.

Because of this, the technology of the foregoing Japanese Laid-OpenPatent Publication 11-311784 sets the retardation axis of the phasecompensation film at the angle intermediate between the upper and loweranchoring directions so as to compensate for the synthetic vector of theupper and lower anchoring directions. However, this construction cannotcompensate for the residual retardation of the liquid crystal layer atthe upper and lower substrates individually and the compensation for theblack representation remains incomplete.

Meanwhile, there is a proposal of a reflection-type liquid crystaldisplay device of vertically aligned (VA)-mode that uses a singlepolarizer (See Japanese Laid-Open Patent Publication 6-337421).

In such a VA-mode liquid crystal display device, the On and Offoperation is just the opposite as in the case of a TN-mode liquidcrystal display device. On the other hand, the operational features of:converting the incoming environmental light to linearly polarized lightby the polarizer; rotating the polarization plane of the linearlypolarized light thus obtained by 90 degrees by using a liquid crystallayer or a phase compensation film having a retardation of about ¼wavelength of visible light; and causing the polarizer to absorb therotated linearly polarized light in the black representation mode, areidentical between the foregoing VA-mode liquid crystal display deviceand the TN-mode liquid crystal display device.

On the other hand, the VA-mode reflection-type liquid crystal displaydevice is advantageous in the point that there remains no liquid crystallayer causing anchoring at the liquid crystal/substrate interface in theblack representation mode contrary to the case of the TN-mode liquidcrystal display device because of the fact that the black representationmode is achieved in the VA-mode reflection-type liquid crystal displaydevice in the state no voltage is applied to the liquid crystal layer.Thereby, the contrast ratio of image representation is improvedsignificantly.

In this way, the VA-mode reflection-type liquid crystal display devicehas an advantageous feature of high contrast ratio and excellentvisibility.

On the other hand, there still exist problems to be solved in such aVA-mode reflection-type liquid crystal display device particularly withregard to the control of alignment of the liquid crystal molecules.

More specifically, a VA-mode liquid crystal display device generallyuses a vertical alignment film, while the performance of such a verticalalignment film may be degraded seriously when subjected to a rubbingprocess. For example, there may be caused defective display of imagessuch as uneven brightness extending in the form of streaks.

Because of this reason, there is a need of achieving alignment controlof liquid crystal molecules in a VA-mode liquid crystal display deviceby means other than rubbing.

In the Japanese Laid-Open Patent Publication 10-301112, for example, thealignment control of the liquid crystal molecules is achieved byproviding a slit extending obliquely in a reflection electrode on theopposite substrate, such that there is induced an oblique electric fieldbetween the upper and lower substrates upon application of a voltage.

This technology, on the other hand, has a drawback in that the overallreflectivity of the pixels is reduced because the part of the liquidcrystal layer located immediately on the slit does not undergo switchingand the visibility of the image representation is not very much improvedeven when the contrast ratio is improved.

Thus, there has been a need of improving the contrast ratio withoutsacrificing the reflectivity in a VA-mode liquid crystal display device.

Meanwhile, a reflection-type liquid crystal display device generally hasa problem of the visibility influenced heavily by the opticalenvironment such that the visibility of the images is degraded seriouslyin the dark optical environment. With this respect, a transmission-typeliquid crystal display device having a backlight provides far superiorvisibility. On the other hand, a transmission-type liquid crystaldisplay device suffers from the problem of poor visibility in the brightoptical environment in that the obtained visibility is inferior to thevisibility achieved by the reflection-type liquid crystal displaydevice.

Thus, in order to improve the foregoing problems, there has beenproposals such as using a front light in combination with areflection-type liquid crystal display device, or a reflection-typeliquid crystal display device having a semi-transparent reflection film.

The approach of using a front light, however, suffers from the problemin that the contrast ratio achieved in the dark optical environment maybe inferior to the contrast ratio of the direct-view typetransmission-type liquid crystal display device. In the bright opticalenvironment, on the other hand, there may arise another problem in thatthe representation becomes dark as compared with the conventionalreflection-type liquid crystal display device because of the existenceof the front light.

In the case of using a semi-transparent film, a metal thin film isgenerally used for this purpose. However, a metal thin film has a largeabsorption coefficient and has a problem in the efficiency ofutilization of light. Further, the metal thin film suffers from theproblem of conspicuous variation of transmittance because of thein-plane variation of film thickness. It should be noted that such ametal thin film is generally provided by a thin Al film having athickness of about 30 nm. Currently, it is difficult for form a metalthin film with uniform thickness over a wide display area.

In order to eliminate the foregoing problem, there has been a proposalin the Japanese Laid-Open Patent Publication 11-281972 in which there isprovided a transparent window by means of a transparent electrode suchas ITO (In₂O₃.SnO₂) at the central part of the pixels. According to thisconventional proposal, the foregoing problems are eliminated and itbecame possible to construct a reflection-transmission-type liquidcrystal display device.

On the other hand, the foregoing conventional proposal of thereflection-transmission-type liquid crystal display device has neededformation of projections and depressions on a planarized film andformation of a step in the transmission region by forming a hole.Further, the foregoing technology requires formation of both thetransparent electrode (ITO) and the reflection electrode (Al) andfurther the formation of a barrier metal film for preventingelectrolytic corrosion, which may be caused at the contacting part ofthe Al pattern and the ITO pattern. Thus, the fabrication process of theliquid crystal display device is complex and the cost of fabricationcould not be reduced.

Further, the conventional reflection-type liquid crystal display device,relying upon the principle of optical switching caused by retardation ofthe liquid crystal layer, has to be designed to have a cell thickness of½ of the wavelength of the visible light in the transmission region anda cell thickness of ¼ of the wavelength of the visible light in thereflection region. However, such a structure has been difficult toproduce.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful liquid crystal display device wherein the foregoingproblems are eliminated.

Another and more specific object of the present invention is to providea reflection-type liquid crystal display device and fabrication processthereof capable of realizing a high reflectivity and high contrastratio.

Another object of the present invention is to provide areflection-transmission-type liquid crystal display device capable ofbeing produced with low cost and having excellent characteristics.

Another object of the present invention is to provide a reflection-typeliquid crystal display device, comprising:

a first substrate;

a second substrate disposed so as to face said first substrate, saidsecond substrate carrying projections and depressions thereon;

a reflective electrode provided on said second substrate so as to coversaid projections and depressions in electrical contact with a switchingdevice provided on said second substrate via a contact hole; and

a liquid crystal layer provided between said first and secondsubstrates, said liquid crystal layer having a negative dielectricanisotropy,

wherein said contact hole is disposed centrally to said reflectionelectrode, and

wherein a structure controlling alignment of liquid crystal molecules insaid liquid crystal layer is disposed so as to overlap said contact holewhen said second substrate is viewed in a direction perpendicularthereto.

According to the present invention, the degradation of reflectivity,caused by the foregoing structure for controlling the alignment of theliquid crystal molecules, is minimized by forming the structure incorrespondence to the contact hole where there is caused a degradationof reflectivity because of the absence of the projections anddepressions.

By forming the contact hole at the central part of the pixel electrodeso as to avoid the peripheral part in which the liquid crystal moleculesare tilted in the inward direction as a result of the action of theoblique electric field, it becomes possible to define four sectors ineach pixel electrode by two hypothetical diagonal lines crossing at thecenter where the foregoing structure is provided.

In such a construction, the liquid crystal molecules of differentalignment directions interfere with each other on the foregoing diagonallines, resulting in an offset in the molecular alignment direction. Onthe other hand, such a construction can successfully eliminate theazimuth dependence of the reflection light by converging the lightincoming to the liquid crystal layer to a circularly polarized light byproviding a phase compensation film having a retardation of about ¼ ofthe visible wavelength. Thereby, the degradation of reflectivity causedby deviation of the azimuth angle of the reflected light is successfullysuppressed.

Another object of the present invention is to provide a method offabricating a reflection-type liquid crystal display device comprising afirst substrate, a second substrate provided so as to face said firstsubstrate, said second substrate carrying thereon projections anddepressions having a reflectivity, a liquid crystal layer having anegative dielectric anisotropy provided between said first and secondsubstrates, and an optically polymerized polymer structure providedbetween said first and second substrates, said method comprising thesteps of:

causing optical polymerization of a compound constituting said polymerstructure by irradiating light perpendicularly to said second substrateand causing reflection of said light by said projections and depressionsin an in-plane direction of said second substrate;

said step of causing optical polymerization is conducted by providing anin-plane directivity to the light reflected by said projections anddepressions by a optimizing a shape of said projections and depressions,such that said optical polymerization is conducted in a directioncorresponding to said in-plane directivity.

According to the present invention, it becomes possible to stabilize thealignment of the liquid crystal molecules by the use of the opticallypolymerized polymer structure formed in the liquid crystal layer at thetime of application of a control voltage. In such an opticallypolymerized polymer structure, the polymer chains can be formed in anarbitrary direction by conducting optical irradiation in the state ofapplying a voltage to the optically polymerized polymers dispersed inthe liquid crystal layer. Thereby, the alignment of the liquid crystalmolecules at the time of application of the voltage is stabilizedbecause of the affinity between the polymer chain and the liquid crystalmolecules.

In the present invention, it should be noted that the projections anddepressions are designed so as to reflect the obliquely incoming lighttoward the observer. When light is directed perpendicularly in such asubstrate, the light is reflected by the projections and depressions inthe in-plane direction of the substrate. Thus, by causing the opticallypolymerizable polymer by the light directed perpendicularly to thesubstrate surface, it becomes possible to form a polymer chaincorresponding to the directivity of reflection. As the liquid crystalmolecules are aligned along the optically polymerizable polymer thusformed, the alignment of the liquid crystal molecules is stabilized.

Another object of the present invention is to provide a reflection-typeliquid crystal display device, comprising:

a first substrate;

a second substrate disposed so as to face said first substrate;

a liquid crystal layer having a negative dielectric anisotropy disposedbetween said first and second substrates; and

a vertical alignment film formed on a surface of said first substrateand a surface of said second substrate,

wherein said alignment film contains a vertical alignment component witha proportion of 25% or more with regard to total diamine components.

According to the present invention, it becomes possible to achieve asufficient contrast ratio even in the case the substrate of thereflection-type liquid crystal display device is the one having areflective projections and depressions thereon, by setting theproportion of the vertical alignment component in the vertical alignmentfilm to be 25% or more with respect to the entire diamine components.

Another object of the present invention is to provide a reflection-typeliquid crystal display device, comprising:

a first substrate;

a second substrate disposed so as to face said second substrate, saidsecond substrate carrying thereon projections and depressions having areflectivity;

a liquid crystal layer having a negative dielectric anisotropy disposedbetween said first and second substrates; and

a polarizer disposed at an outer side of said first substrate such thatan absorption axis of said polarizer extends generally parallel to adirection in which a reflection intensity caused by said projections anddepressions becomes maximum.

According to the present invention, it becomes possible to improve thecontrast ratio of the liquid crystal display device by setting thedirection of the absorption axis of the polarizer to be generallycoincident with the direction in which the reflection intensity of thereflection from the projections and depressions becomes maximum. Thepresent invention utilizes the phenomenon that the optical absorptionefficiency of the polarizer is higher in the direction of the opticalabsorption axis, in which direction the polarizing components such aiodine or dichroic dyes are aligned, than other directions. By aligningthe direction of the polarizer in which the efficiency of opticalabsorption is maximum to be coincident with the direction in which thereflection from the depressions and projections is the strongest, thepresent invention suppresses the brightness at the time of the blackrepresentation mode further.

Of course, such a setting of the absorption axis of the polarizerresults in a decrease of brightness also in the white representationmode. In the case of the reflection-type liquid crystal display devicehaving the reflective projections and depressions thereon, on the otherhand, actual degradation of brightness in the white representation modeis suppressed minimum because the light from every direction isreflected in the direction perpendicular to the substrate. Thus, thepresent invention can achieve the improvement of contrast ratio withoutsacrificing the brightness of the reflection-type liquid crystal displaydevice.

Another object of the present invention is to provide a reflection-typeliquid crystal display device, comprising:

a first substrate;

a second substrate disposed so as to face said first substrate, saidsecond substrate carrying projections and depressions having areflectivity;

a liquid crystal layer having any of positive or negative dielectricanisotropy provided between said first and second substrates; and

a polarizer disposed at an outer side of said first substrate,

an optical phase compensation film disposed between said first substrateand said polarizer, said optical phase compensation film having anegative electric anisotropy in a direction perpendicular to a plane ofsaid first substrate,

said optical phase compensation film having a retardationdf{(n_(x)+n_(y))/2−n_(z)} so as to satisfy the relationship0.4≦[df{(n _(x) +n _(y))/2−n _(z)}]/(dlcΔn)≦0.7,wherein n_(x), n_(y) and n_(z) are refractive indices of said opticalphase compensation film respectively in an x-direction, a y-directionand a z-direction, dlc is the thickness of said liquid crystal layer,and Δn is a refractive index difference between an extraordinary ray andan ordinary ray in the liquid crystal layer.

According to the present invention, it is possible to compensate for theleakage light formed at the time of the black representation modesubstantially completely in a reflection-type liquid crystal displaydevice having a substrate carrying thereon reflective projections anddepressions for the case in which the foregoing projections anddepressions are optimized so as to incorporate as much environmentallight as possible within a limitation that there is caused no interfacereflection.

Another object of the present invention is to provide areflection-transmission-type liquid crystal display device, comprising:

a first substrate;

a second substrate provided so as to face said first substrate;

a transparent electrode provided on a surface of said first substratefacing said second substrate;

a reflection electrode provided on a surface of said second substratefacing said first substrate, said reflection electrode having anopening;

a scattering layer provided between said first and second substrates,said scattering layer including therein a liquid crystal layer andchanging an optical state thereof between a scattering state and anon-scattering state; and

a pair of polarizers disposed at outer sides of a liquid crystal panelformed by said first substrate, said second substrate and saidscattering layer,

at least one of said polarizers is formed of a circular polarizer.

According to the present invention, optical switching between a whiterepresentation mode and a black representation mode is achieved by atransition of state of a polymer-dispersed liquid crystal between thescattering state and the non-scattering state. Thus, there is no need ofproviding a thick planarizing film having an opening acting as anoptical window for securing a thickness for a liquid crystal layerrequired for optical switching in the transmission region, contrary tothe conventional reflection-transmission-type liquid crystal displaydevice. Further, there is no need of forming a scattering structure on aplanarized surface. Further, there is no need of forming a transparentelectrode corresponding to the optical window opening. In the presentinvention, it is sufficient to provide a reflection electrode having anoptical passage such as a slit. Thus, according to the presentinvention, the construction of the reflection-transmission-type liquidcrystal display device is significantly simplified.

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the construction of a pixel region of areflection-type VA-mode liquid crystal display device according to afirst embodiment of the present invention;

FIG. 2 is a diagram showing a cross-sectional structure of thereflection-type VA-mode liquid crystal display device of FIG. 1;

FIG. 3 is a diagram showing the domain structure formed in thereflection-type VA-mode liquid crystal display device of FIG. 1;

FIG. 4 is a diagram showing the construction of a comparative experimentof the reflection-type VA-mode liquid crystal display device;

FIG. 5 is a diagram showing an example of black representation mode inthe reflection-type liquid crystal display device of FIG. 1;

FIG. 6 is a diagram showing a modification of the reflection-type liquidcrystal display device of FIG. 1;

FIG. 7 is a cross-sectional diagram showing the construction of areflection-type liquid crystal display device according to a secondembodiment of the present invention;

FIG. 8 is a diagram showing the directivity of the reflection lightformed in the reflection-type liquid crystal display device of FIG. 7;

FIG. 9 is a diagram showing the directivity of the reflection lightformed in the reflection-type liquid crystal display device of FIG. 1;

FIG. 10 is a diagram showing the cross-sectional structure of areflection-type liquid crystal display device according to a thirdembodiment of the present invention;

FIG. 11 is a diagram showing the cross-sectional structure of areflection-type liquid crystal display device according to a fourthembodiment of the present invention;

FIG. 12 is a diagram showing reflection of incident light in thereflection-type liquid crystal display device of FIG. 11;

FIGS. 13A and 13B are diagrams showing examples of refractive indexellipsoid respectively for the phase compensation film and liquidcrystal layer used in the reflection-type liquid crystal display deviceof FIG. 12;

FIGS. 14A and 14B are diagrams showing the cross-sections of therefractive indices ellipsoid of FIGS. 13A and 13B, respectively;

FIG. 15 is a diagram showing the azimuth dependence of reflectivity ofthe reflection-type liquid crystal display device of the presentinvention in the black representation mode together with a comparativeexperiment;

FIG. 16 is a diagram showing the azimuth dependence of contrast ratio ofthe reflection-type liquid crystal display device of the presentinvention together with a comparative experiment;

FIG. 17 is a diagram showing the construction of a conventionalreflection-transmission type liquid crystal display device;

FIG. 18 is a diagram showing a first construction of areflection-transmission-type liquid crystal display device according toa fifth embodiment of the present invention;

FIGS. 19A and 19B are diagrams showing the operational principle of thereflection-transmission-type liquid crystal display device of FIG. 18;

FIG. 20 is a diagram showing a second construction of areflection-transmission-type liquid crystal display device according thefifth embodiment of the present invention;

FIGS. 21A and 21B are diagrams showing the operational principle of thereflection-transmission-type liquid crystal display device of FIG. 20;

FIG. 22 is a diagram showing an example of a driving method used in thefifth embodiment of the present invention;

FIG. 23 is a diagram showing another example of the driving method usedin the fifth embodiment of the present invention;

FIG. 24 is a diagram showing a further example of the driving methodused in the fifth embodiment of the present invention;

FIGS. 25A and 25B are diagrams showing an example of a TFT substrateused in the present embodiment;

FIG. 26 is a diagram showing the operational characteristics of thereflection-transmission-type liquid crystal display device of thepresent embodiment;

FIG. 27 is a diagram showing the construction of a color filter used inthe reflection-transmission-type liquid crystal display device of thepresent embodiment;

FIG. 28 is a diagram showing another construction of the color filterused in the reflection-transmission-type liquid crystal display deviceof the present invention; and

FIG. 29 is a diagram showing a further construction of the color filterused in the reflection-transmission-type liquid crystal display deviceof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment

FIGS. 1 and 2 show respectively the plan view and a cross-sectional viewof a reflection-type liquid crystal display device 10 according to afirst embodiment of the present invention for the part corresponding toone pixel.

Referring to FIGS. 1 and 2, the reflection-type liquid crystal displaydevice 10 is basically formed of a lower glass substrate 11, an upperglass substrate 14 facing the lower glass substrate 11, and a liquidcrystal layer 13 having a negative dielectric anisotropy confinedbetween the substrates 11 and 14, and the lower glass substrate 11carries thereon a TFT (thin-film transistor) 11A and further a gateelectrode 11B and a data electrode 11C cooperating with the TFT 11A. Forthe glass substrate 11, it is possible to use a conventional TFTsubstrate used in transmission-type liquid crystal display panels. Inthis case, a pixel electrode 11D of a transparent conductor such as ITOis provided on the glass substrate 11 in the state connected to the TFT11A electrically.

The TFT 11A, the gate electrode 11B and the date electrode 11C arecovered by an insulating film 11E such as a resin, and a projection anddepression pattern 12 of a resist layer is provided on the foregoinginsulating film 11E, wherein the projection and depression pattern 12forms projections and depressions on the insulating film 11E.

The projection and depression pattern 12 is covered with a reflectionelectrode 12A, wherein the reflection electrode 12A is connectedelectrically to the pixel electrode 11D at the central part of the pixelregion by way of a contact hole 11F formed in the insulating film 11E.

The reflection electrode 12A forms projections and depressions incorrespondence to the projection and depression pattern 12 except forthe part thereof corresponding to the contact hole 11F, and thus, thereis formed a flat region in the pixel region at the central part thereofcorresponding to the contact hole 11F.

On the opposing substrate 14, on the other hand, there is formed anopposing electrode 14A at the side thereof facing the substrate 11uniformly and continuously, and there is formed an alignment controlstructure 12B on the opposing electrode 14A in the part thereofcorresponding to the contact hole 11F by a resin or a dielectricmaterial having a dielectric constant smaller than the dielectricconstant of the liquid crystal layer 13, for controlling the alignmentdirection of the liquid crystal molecules 13A in the liquid crystallayer 13.

Further, there is formed a vertical alignment film 12C on the substrate11 so as to cover the projection and depression pattern 12 and thereflection electrode 12A, and another vertical alignment film 12D isprovided on the substrate 14 so as to cover the opposing electrode 14Aand the alignment control structure 12B.

It should be noted that the alignment films 12C and 12D function so asto align the liquid crystal molecules 13A in the liquid crystal layer 13in the direction generally perpendicular to the substrate 11 or 14 asillustrated in FIG. 2 by dotted lined in the non-activated state of thepixel in which no drive electric field is applied to the liquid crystallayer 13. On the other hand, because there is formed the alignmentcontrol structure 12B at the central part of the pixel in the liquidcrystal display device 10 of FIGS. 1 and 2, the liquid crystal moleculesare tilted toward the alignment control structure 12B, and as a result,there are formed domains A-D in the pixel region as represented in FIG.3 in which the liquid crystal molecules are tilted in the directionindicated by the arrows.

Further, on the outer side of the substrate 14, there is formed a TAC(triacetate cellulose) film 15 having a retardation of about 100 nm inthe thickness direction, and a phase compensation film 16 having aretadation of about ¼ of the visible wavelength and a polarizer 17 arelaminated on the TAC film 15 consecutively.

In the reflection-type liquid crystal display device 10 of FIGS. 1 and2, the environmental light incident obliquely to the polarizer 17 isconverted to a linear polarized light by the polarizer 17 and incidentto the liquid crystal layer 13 after being converted to a circularlypolarized light by the ¼-wavelength film 16.

In the non-activated state of the liquid crystal display device 10 inwhich there is no voltage applied across the reflection electrode 12Aand the opposing electrode 14A, it should be noted that the liquidcrystal molecules 13A are aligned generally perpendicularly to thesubstrate 11 or 14 in the liquid crystal layer 13 as represented in FIG.2, and the circularly polarized light incident to the liquid crystallayer 13 is reflected by the reflection electrode 12A. Thereby, thereflected light passes consecutively through the liquid crystal layer13, the TAC film 15 and the ¼-wavelength film 16 consecutively in thereverse direction and is converted to a linearly polarized light havingthe polarization plane rotated by 90 degrees with regard to the initialpolarization plane. Thereby, the linearly polarized light is cut off bythe polarizer 17.

In the case a drive voltage is applied across the reflection electrode12A and the opposing electrode 14A, on the other hand, the liquidcrystal molecules 13A in the liquid crystal layer 13 are alignedgenerally parallel to or obliquely to the liquid crystal layer 13, andthe circularly polarized light incident to the liquid crystal layer 13through the ¼-wavelength film 16 and the TAC film 15 is converted tolinearly polarized light by the retardation of the liquid crystal layer13. The linearly polarized light thus formed is then reflected by thereflection electrode 12A and is passed through the ¼-wavelength film 16and the TAC film 15 in the reverse direction consecutively. Thereby, thereflected linearly polarized light is converted to linearly polarizedlight having a polarization plane identical with the polarization planeof the linearly polarized light converted from the incident light at thepolarizer 17, and the linearly polarized light thus obtained is exitedthrough the polarizer 17.

In the reflection-type liquid crystal display device 10 of such aconstruction, it should be noted that there is formed no projection anddepression pattern 12 in the part corresponding to the contact hole 11Fas a result of formation of the contact hole 11F in the reflectionelectrode 12A, and thus, the environmental light incident to thesubstrate 14 obliquely is not reflected back to the observer in the partof the reflection electrode 12A where the contact hole is formed.Because of this, the problem of degradation of reflectivity at thecentral part of the pixel cannot be avoided in the reflection-typeliquid crystal display device 10 having the construction of FIGS. 1 and2.

Further, optical loss caused by the alignment control structure 12Bcannot be avoided even though the alignment control structure 12B isformed of a transparent resin for minimizing the optical loss.

Thus, in a structure such as the one shown in FIG. 4 in which thealignment control structure 12B is formed at the central part of thepixel region and the contact hole 11F is formed in the vicinity of a TFT11C provided at the peripheral part of the pixel region, it isinevitable that there are formed plural regions of low reflectivity inthe pixel region when viewed in the direction perpendicular to thesubstrate 14. In such a structure, the brightness of the imagerepresentation is deteriorated seriously.

In the case of the liquid crystal display device 10 of FIGS. 1 and 2, onthe other hand, the alignment control structure 12B coincides with thecontact hole 11F when viewed in the direction perpendicularly to thesubstrate 14, and the degradation of reflectivity is suppressed minimum.

Further, as can be seen from the cross-sectional view of FIG. 2, thereis formed a depression in the region of the contact hole 11F incorrespondence to the projecting alignment control structure 12B, suchthat the depression has a lateral size and a width respectivelycorresponding to a lateral size and a width of the alignment controlstructure 12B. As a result, substantially the same cell thickness ismaintained also in such a region where the projecting alignment controlstructure 12B is formed.

Next, fabrication process of the reflection-type liquid crystal displaydevice 10 of FIGS. 1 and 2 will be explained.

In the present embodiment, a substrate produced for a transmission-typeliquid crystal display device is used for the TFT substrate 11, andthus, the TFT substrate 11 carries thereon the TFT 11A, the gateelectrode 11B, the date electrode 11C and the transparent pixelelectrode 11D. The TFT substrate 11 is then formed with a resist layerby applying a positive resist film by a spin-coating process with athickness of about 1.2 μm such that the positive resist film covers theTFT 11A, the gate electrode 11B, the date electrode 11C and thetransparent pixel electrode 11D.

The resist layer thus formed has a flat surface, and ultravioletirradiation process is conducted, after applying a prebaking process at90° C. for 30 minutes, for forming the projection and depression pattern12 by using a mask, except for the central part of the pixel region, inwhich the contact hole is to be formed.

By developing the resist layer thus exposed, followed by conducting afinal baking process at 200° C. for 60 minutes, the projection anddepression pattern 12 is formed.

The projection and depression pattern 12 thus formed is then coated withan Al film by conducting an evaporation deposition process, and thereflection electrode 12A for the pixel region is formed by patterningthe Al film thus formed by applying a photolithographic process.

Next, formation of the alignment control structure 12B will beexplained.

First, a positive photosensitive transparent resin layer having adielectric constant of 3.2 is applied to the substrate 14 with athickness of about 1.2 μm by a spin coating process so as to cover theelectrode 14A.

Next, the resin layer thus formed is subjected to a prebaking process at90° C. for 30 minutes, followed by an ultraviolet exposure process thatuses a mask. Further, by consecutively conducting a developing process,a post-exposure process, a first baking process at 130° C. for 2minutes, and further a final baking process at 220° C. for 6 minutes,the foregoing alignment control structure 12B is formed at the centralpart of the pixel region.

Further, vertical alignment films 12C and 12D each containing a sidechain diamine are applied respectively on the surface of the TFTsubstrate 11 and the opposing substrate 13 such that the verticalalignment film 12C covers the projection and depression pattern 12 andthe reflection electrode 12A and such that the vertical alignment film12D covers the electrode 14A and the alignment control structure 12B.

Next, the substrates 11 and 14 thus prepared are stacked with each othervia a spacer having a diameter of 3 μm therebetween, and a liquidcrystal having a negative dielectric anisotropy (Δ∈=−3.5) characterizedby a refractive index difference Δn between the extraordinary ray andthe ordinary of 0.067 is injected into the gap formed between thesubstrates 11 and 14. Thereby, a liquid crystal panel of verticalalignment mode is formed.

Further, by stacking the TAC film 15, the ¼ wavelength film 16 and thepolarizer 17 consecutively on the outer surface of the substrate 14, thefabrication process of the reflection-type liquid crystal display device10 is completed.

FIG. 5 is a diagram showing the state of the black representation modein the liquid crystal display device 10 of the present embodiment forthe case the proportion of the vertical alignment component (side chaindiamine) in the vertical alignment films 12C and 12D with regard to theentire amine component is set to 5%, 10% and 25%.

Referring to FIG. 5, it can be seen that there is caused an extensiveleakage of light in the case the proportion of the vertical alignmentcomponent in the vertical alignment film is set to 5% or 10%, andassociated with such a leakage of light, there is caused the problem ofdegradation of contrast ratio.

On the other hand, in the case the proportion of the vertical alignmentcomponent in the alignment films 12C and 12D is 25%, it can be seen thatthere is little leakage of light. Thus, from the result of FIG. 5, it isconcluded that the proportion of the vertical alignment component in thevertical alignment films 12C and 12D should be preferably set to 25% ormore.

Generally, leakage of light is caused whenever the liquid crystalmolecule is tilted however small the tilt angle may be. However, it isthought that recognition of such light leakage by human beings occurswhen the tilt angle of the liquid crystal molecules has exceeded acertain threshold.

In the case of a transmission-type liquid crystal display device inwhich no projections or depressions are formed on the surface, asufficient contrast ratio is achieved when the proportion of thevertical alignment component in the molecular orientation film is 5%. Onthe other hand, the result of FIG. 5 shows that a sufficient contrastratio cannot be secured in the reflection-type liquid crystal displaydevice unless the proportion of the vertical alignment component in thealignment film is set to be 25% or more.

Table 1 below explains the reflectivity (brightness) and contrast ratioobtained for the white representation mode in the reflection-type liquidcrystal display device 10 as viewed in the direction perpendicular tothe liquid crystal panel, in comparison with the result for thereflection-type liquid crystal display devices according to comparativeexperiments 1 and 2 (Comparative 1, Comparative 2), wherein themeasurement of Table 1 is conducted by using an integrating sphereoptical source. In the comparative experiment 1, on the other hand, thereflection-type liquid crystal display device uses an oblique slit inthe opposing electrode 14A in place of the alignment control structure12B while in the comparative experiment 2, the reflection-type liquidcrystal display device uses an alignment control structure similar tothe alignment control structure 12B on the substrate 14 but with aheight of 2.0 μm.

TABLE 1 VA component % brightness % contrast Embodiment 1 5 13 2.6 10 1311.0 25 13 23.0 50 13 23.3 Comparative 1 50 10 17.7 Comparative 2 50 1221.2

Referring to Table 1, it can be seen that the reflection-type liquidcrystal display device 10 of the present embodiment achieves brightnesssuperior to the liquid crystal display device of any of the comparativeexperiments 1 and 2, although the proportion of the vertical alignmentcomponent (side chain diamine) with regard to the total diaminecomponent is changed in the range of 5-50% in the present embodiment.Further, it can be seen that a contrast ratio of 23.0 or more isachieved by setting the proportion of the vertical alignment componentto be 25% or more.

Considering the fact that a TN-mode reflection-type liquid crystaldisplay device can provide brightness of only about 13% and contrastration of 18 in the maximum, it will be understood that thereflection-type liquid crystal display device 10 of the presentembodiment can provide much superior performance as compared with such aTN-mode reflection-type liquid crystal display device.

In Table 1, it is noted that the brightness of the white representationmode is reduced by about 30% in the case of the reflection-type liquidcrystal display device of the comparative experiment 1 over thereflection-type liquid crystal display device 10 of the presentembodiment. It is believed that this result is caused by the effect thatthe liquid crystal molecules in the vicinity of the slit formed in theopposing electrode does not cause switching.

In the comparative experiment 2, it is also noted that the achievedbrightness is smaller than the brightness achieved by the presentembodiment by about 8%. It is believed that this has been caused as aresult of reduced retardation of the liquid crystal layer in the partlocated on the alignment structure. It should be noted that thealignment structure in the comparative experiment 2 is has a heightlarger than the alignment structure used in the present embodiment.

In the reflection-type liquid crystal display device 10 of the presentembodiment, it is also possible to form an alignment control structure12B, in the case a material having a dielectric constant larger than thedielectric constant of the liquid crystal layer 13 is used for thealignment control structure 12B, such that the alignment controlstructure 12B fills the depression formed on the side of the TFTsubstrate 11 in correspondence to the conductive plug 11F as representedin FIG. 6. According to such a construction, it is also possible torealize the molecular alignment of the liquid crystal molecules tiltingtoward the center of the pixel region.

Second Embodiment

Next, explanation will be made on a reflection-type liquid crystaldisplay device 20 according to a second embodiment of the presentinvention.

FIG. 7 shows the construction of the reflection-type liquid crystaldisplay device 20 wherein those parts corresponding to the partsdescribed previously are designated by the same reference numerals andthe description thereof will be omitted.

Referring to FIG. 7, the reflection-type liquid crystal display device20 has a construction somewhat similar to that of the reflection-typeliquid crystal display device 10 explained previously, except that thealignment control structure 12B is removed from the substrate 11 or 14.

Instead, there are formed polymer chains 13B having an orientation inthe liquid crystal layer 13 in the liquid crystal display device 20 ofthe present embodiment, wherein the polymer chains 13B function so as tocause tilting of the liquid crystal molecules 13A toward the centralpart of the pixel region. In FIG. 7, it should be noted that thereference numeral 13B merely represents the polymer chains schematicallyand is not intended to depict the actual structure of the polymer chainsor indicate individual polymer chains.

In more detail, the projection and depression pattern 12 is formed onthe TFT substrate 11 in the present embodiment in the form of anelongated pattern such that each projection pattern extends in thelongitudinal direction or lateral direction of the substrate asrepresented in FIG. 8. Further, the alignment films 12C and 12D areformed by using a vertical alignment film containing the verticalalignment component with a proportion of 25%.

Referring to FIG. 8, the projections and depressions in the projectionand depression pattern 12 are formed in each of the domain regions A-Dschematically represented in FIG. 3, wherein each of the projections ordepressions extends in the longitudinal direction or lateral directionalong the outer peripheral edge of the regions A-D.

Further, the substrate 11 and the substrate 12 are stacked with eachother via a spacer having a diameter of 3 μm, and a liquid crystaladmixed with a resin forming a polymer chain upon ultravioletirradiation is injected into the gap formed between the substrates 11and 14. The liquid crystal may contain the resin with a proportion of0.3% by weight. With this, the liquid crystal layer 13 is formed. In thepresent embodiment, a resin that causes photo-polymerization uponirradiation of ultraviolet radiation (I-line) with the intensity of 2000mJ/cm² or more is used.

In the reflection-type liquid crystal display device thus formed, itwill be noted that the intensity of the reflection light formed by theprojections and depressions in the projection and depression pattern 12increases in the longitudinal direction and in the lateral direction ofthe substrate as represented in FIG. 8, by forming the laterally orlongitudinally elongating projection and depressions on the TFTsubstrate 11. In the projection and depression pattern 12 of FIG. 1, onthe other hand, no such a directivity appears in the reflected light asrepresented in FIG. 9.

Thus, in the present embodiment, a drive voltage of 4V is applied to theliquid crystal display device thus obtained, and ultraviolet radiationis applied to the substrate 14 in this state such that the intensity ofthe reflected light, reflected by the projection and depression pattern12 becomes 2000 mJ/cm² or more in the liquid crystal layer 13 in thelongitudinal direction and in the lateral direction. As a result of theaction of the reflected light formed from the ultraviolet radiation inthe longitudinal direction and lateral direction, there are formedpolymer chains 13B in the liquid crystal layer 13 extending in thelongitudinal and lateral directions of the substrate, and the liquidcrystal molecules 13A in the liquid crystal layer 13 are aligned asrepresented in FIG. 2 as a result of the action of the verticalalignment films 12C and 12D and further the polymer chains 13B thusformed.

The measurement of brightness and contrast ratio conducted on thereflection-type liquid crystal display device thus formed revealedsimilar results as in the case of the reflection-type liquid crystaldisplay device 10 of the previous embodiment.

According to the present embodiment, it is possible to polymerize aphoto-polymerizable compound in an arbitrary direction in which theoptical intensity becomes maximum, by controlling the shape of theprojection and depression pattern 12 reflecting the ultravioletradiation and by incorporating the photo-polymerizable compound into theliquid crystal layer 13.

Third Embodiment

FIG. 10 shows the construction of a reflection-type liquid crystaldisplay device 30 according to a third embodiment of the presentinvention, wherein those parts corresponding to the parts describedpreviously are designated by the same reference numerals and thedescription thereof will be omitted.

Referring to FIG. 10, the liquid crystal display device has aconstruction mixing the features of the first embodiment and the secondembodiment in that the glass substrate 14 carries thereon the alignmentcontrol structure 12B and that the projections in the projection anddepression pattern 12 have an elongated form extending in thelongitudinal or lateral direction of the substrate as represented inFIG. 8. Further, the liquid crystal layer 13 includes therein theoptically polymerized chains 13B.

In the liquid crystal display device 30 of FIG. 10, it should be notedthat the absorption axis of the polarizer 17 is set in the longitudinaldirection of the substrate and the direction of the retardation axis ofthe ¼ wavelength film 16 is set to form an angle of 45 degrees withrespect to the absorption axis of the polarizer 17.

Table 2 below compares the brightness and contrast ratio obtained forthe reflection-type liquid crystal display device 30 thus obtained inthe white representation mode with the brightness and contrast ratioobtained for a similar reflection-type liquid crystal display device(comparative example 3: Comparative 3), in which the direction of theabsorption axis of the polarizer 17 is offset from the longitudinaldirection of the substrate by 45 degrees.

TABLE 2 VA component % brightness % contrast Embodiment 3 25 13 24.8Comparative 3 25 13 23.0

Referring to Table 2, it will be noted that there is no substantialchange with regard to brightness between the present embodiment and thecomparative experiment, while it will also be noted that there is animprovement of contrast ratio in the liquid crystal display device ofthe present embodiment.

It is believed that this improvement is achieved as a result ofimprovement of the black representation mode, which in turn is caused asa result of setting the absorption axis of the polarizer 17 in thedirection in which the reflection intensity of the projection anddepression pattern 12 becomes maximum.

Fourth Embodiment

FIG. 11 shows the construction of a reflection-type liquid crystaldisplay device 40 according to a fourth embodiment of the presentinvention while FIG. 12 shows the propagation of rays in thereflection-type liquid crystal display device 40 of FIG. 11. In FIG. 12,it should be noted that only those parts related to the optical pathlength of the optical rays is represented and representation of otherparts are omitted.

Referring to FIG. 11, the liquid crystal display device 40 of thepresent embodiment is generally formed of a lower glass substrate 41, anupper glass substrate 44 facing the lower glass substrate 41 and aliquid crystal layer 43 having a negative dielectric anisotropy confinedbetween the upper and lower glass substrates 41 and 44, wherein thelower glass substrate 44 carries thereon elements such as a TFT notillustrated, a gate electrode 41C cooperating with the TFT, and furthera data electrode not illustrated. A standard TFT substrate designed fora transmission-type liquid crystal display device can be used for theglass substrate 44. In this case, a pixel electrode 41D of a transparentconductor such as ITO is formed on the glass substrate 41 in the stateconnected to the TFT electrically.

It should be noted that the TFT, the gate electrode 41C and the dateelectrode are covered by an insulating film such as a resin, and thereis formed a projection and depression pattern 42 on the insulating film41E by patterning and processing a resist film.

The projection and depression pattern 42 is covered by a reflectionelectrode 42A of Al and the like, and the reflection electrode isconnected to the pixel electrode 41D via a contact hole 41F formed inthe insulation film 41E preferably at the central part of the pixelregion.

On the upper glass substrate 44, there is formed an opposing electrode44A uniformly and continuously at the surface of the substrate 44 facingthe substrate 41.

Further, there is formed a vertical alignment film 42C on the substrate41 so as to cover the projection and depression pattern 42 and thereflection electrode 42A and another vertical alignment film 42D isformed on the substrate 44 so as to cover the opposing electrode 44A.

In the non-activated state in which there is no drive electric fieldapplied to the liquid crystal layer 43, the alignment films 42C and 42Dact to align the liquid crystal molecules in the direction generallyperpendicular to the substrate 41 or 44, while the liquid crystalmolecules contacting the projection and depression pattern 42 causetilting as represented in FIG. 12 because of the existence of theprojection and depression pattern 42.

Further, a phase compensation film 45 preferably formed of a TAC film isformed on the outer side of the substrate 44, and a ¼ wavelength film 46and a polarizer 47 are laminated consecutively further on thecompensation film 45.

In the reflection-type liquid crystal display device 40 of the presentembodiment, it should be noted that the liquid crystal molecules 43Aconstituting the liquid crystal layer 43 is not limited to the onehaving a negative dielectric anisotropy but also may be the one having apositive dielectric anisotropy. Even in such a case, the liquid crystaldisplay device 40 is a reflection-type liquid crystal display devicebecause of the fact that the liquid crystal molecules 43A are aligned inthe direction generally perpendicular to the plane of the substrate 41or 44 in the non-activated state thereof.

In the reflection-type VA-mode liquid crystal display devices 10-30explained in the preceding embodiments, it should be noted that theliquid crystal layer 13 shows a retardation also in the non-activatedstate of the device in view of the fact that the environmental lightimpinges obliquely to the liquid crystal layer 13 and in view of thefact that the liquid crystal molecules 13A are tilted by the projectionand depression pattern 42. Thus, the desired ideal black representationcannot be achieved in the non-activated state of the foregoingreflection-type VA-mode liquid crystal display device, unless theretardation of the liquid crystal layer 13 in the non-activated state iscompensated for by the phase compensation film and the like.

In the case of a transmission-type VA-mode liquid crystal displaydevice, there is already a proposal of the technology for compensatingfor the retardation of a vertically aligned liquid crystal layer byusing a phase compensation film in the British Patent 1462978 or in theJapanese Laid-Open Patent Publication 10-153802.

In these proposals, the retardation of a phase compensation film givenas df·{(n_(x)+n_(y))/2−n_(z)} is set to be generally equal to theretardation of the liquid crystal layer defined as dlc·Δn, wherein dfrepresents the thickness of the phase compensation film, n_(x), n_(y)and n_(x) respectively represent the refractive indices of the phaseretardation film in the x-, y- and z- directions, dlc represents thethickness of the liquid crystal layer, and Δn represents the refractiveindex difference between the extraordinary ray and the ordinary ray inthe liquid crystal layer.

In such a technology of transmission-type VA-mode liquid crystal displaydevice, the phase compensation film is used merely for blocking thelight incident obliquely in the black representation mode and forimproving the viewing angle, and the desired compensation of the blackrepresentation mode is not attained when applied to a reflection-typeVA-mode liquid crystal display device.

It should be noted that a reflection-type VA-mode liquid crystal displaydevice having projections and depressions on a reflection surface isdesigned so as to incorporate as much environmental light as possibleand reflect the incorporated environmental light toward the observer.

Referring to FIG. 12, the environmental light incident obliquely with anincident angle θ1 is refracted with a refraction angle θ2 determined bythe refractive index ratio between the air and the phase compensationfilm and impinges into the liquid crystal layer 43 with an incidentangle θ3.

At the interface between the liquid crystal layer 43 and the substrate44, the liquid crystal molecules 43A are controlled the alignment statethereof by the vertical alignment film 42D not illustrated in FIG. 12 inthe direction generally perpendicular to the plane of the substrate 44.Because of this, the incident light hits the liquid crystal molecule 43Awith the angle of θ3 in the vicinity of the interface between the liquidcrystal layer 43 and the substrate 44. Here, it should be noted that therefractive index of the liquid crystal layer is about 1.5 and isapproximately identical to the refractive index of the phasecompensation film 45. Because of this, it is possible to regard that theincident angle θ3 is nearly equal to the incident angle θ2.

On the other hand, in such a reflection-type VA-mode liquid crystaldisplay device, it is necessary to emit the obliquely incidentenvironmental light in the direction perpendicularly to the substrate 44as explained with reference to preceding embodiments, and or thispurpose, there is formed the projection and depression pattern 42 on theTFT substrate 41.

In FIG. 12, such a projection and depression pattern 42 is approximatedby a cone having a cross-section of an isosceles triangle. Thus, on theprojection and depression pattern 42, the liquid crystal molecules 43Aare aligned perpendicularly to the oblique edge of the triangle thatforms an angle ζ with regard to the plane of the substrate 41 as aresult of the function of the vertical alignment film 42C covering theprojection and depression pattern 42.

Thus, in the liquid crystal layer 43, the liquid crystal molecules 43Aincreases the tilt angle gradually in the thickness direction of theliquid crystal layer 43 from the value of 0 at the interface between theliquid crystal layer 43 and the substrate 44 to the value of ζ at theinterface between the liquid crystal layer 43 and the projection anddepression pattern 42. Thus, in the vicinity of the interface betweenthe liquid crystal layer 43 and the substrate 41, the incident angle ofthe light impinging to the liquid crystal molecule 43A is decreased fromthe foregoing angle θ3 by the angle ζ because of the tilt caused in theliquid crystal molecule 43A by the projection and depression pattern43A.

Thus, the incident light entering into the liquid crystal layer 43 fromthe phase compensation film 45 hits the projection and depressionpattern 42 with an incident angle ζ and reflected also with a reflectionangle ζ. As a result, the reflected light again hits the liquid crystalmolecule 43A aligned perpendicularly on the projection and depressionpattern 42 with an incident angle ζ.

At the interface between the liquid crystal layer 43 and the substrate41, the alignment direction of the liquid crystal molecules iscontrolled perpendicularly to the plane of the substrate 41. Thus, theliquid crystal molecules 43A change the alignment direction in thethickness direction of the liquid crystal layer 43 gradually from thesubstrate 41 to the substrate 44. Associated with this, the incidentangle of the reflection light incident to the liquid crystal molecules43A is reduced gradually and becomes zero at the interface to thesubstrate 44.

In the optical system of FIG. 12, the optical path length within thephase compensation film 45 in the first half part of the optical path,defined as the optical path of the incident light reaching theprojection and depression pattern 42, is given as dv/cos θ2, whereinthis optical path length is approximated to be equal to dv/cos2ζ in viewof the relationship θ2≈θ3 (dv/cosθ2≈dv/cos2ζ). Further, the optical pathlength of the incident light in the liquid crystal layer 13 is given asdlc/cos2ζ. On the other hand, the optical path length of the reflectionlight reflected vertically to the principal plane of the substrate 41 bythe projection and depression pattern 42 is given as dlc in the liquidcrystal layer and dv in the phase compensation film 45.

Thus, in the case of the reflection-type VA-mode liquid crystal displaydevice 40 in which the environmental light enters obliquely, it will benoted that there is caused a retardation even in the non-activated stateof the liquid crystal display device because of the different opticalpath lengths between the incoming optical path and outgoing opticalpath, and that the magnitude of the retardation depends on the incidentangle θ1 and the angle ζ of the projection and depression pattern 42.

In an example in which the liquid crystal layer 43 has a thickness dlcof 3 μm and a refractive index difference Δn of 0.067 and in which theprojection and depression pattern 42 provides an average inclinationangle <ζ> of 13 degrees, the retardation of the liquid crystal layer 43in the non-activated state in which no drive voltage is applied to theliquid crystal display device is calculated to be 33 nm as representedin Case A of Table 3 below, provided that the incident angle θ1 of theincident light is set to 25 degrees.

TABLE 3 retardation of liquid phase crystal difference reflector <ζ>layer {circle around (1)} compensation A 13.06 33.25 15.26 45.9% B 8.9815.98 9.05 56.6% C 7.67 13.01 7.92 60.9% D 7.48 11.87 7.53 63.4%reflector phase difference{circle around (2)} compensation A 29.65 89.2% B 16.15 101.1% C 13.71 105.4% D 12.85 108.3% reflector phasedifference{circle around (3)} compensation A 36.32 109.2% B 19.04 119.1%C 15.94 122.5% D 14.82 124.9% reflector phase difference{circle around(4)} compensation A 51.34 154.4% B 25.96 162.5% C 21.42 164.6% D 19.76166.5%

In Table 3, it should be noted that Cases B, C and D are cited inaddition to Case A, wherein Case B represents the case in which theaverage inclination angle <ζ> is set to 9 degrees, Case C represents thecase in which the average inclination angle <ζ> is set to 7.7 degrees,and Case D represents the case in which the average inclination angle<ζ> is set to 7.5 degrees.

In order to compensate for such retardation caused obliquely in theliquid crystal layer 43, it is possible to use a film having a negativedielectric anisotropy in the direction perpendicular to the substrate.

Thus, Table 1 further shows the retadation value in the obliquedirection and the efficiency of compensation for those cases in whichthe phase compensation film 45 has a refractive index difference{(n_(x)+n_(y))/2−n_(z)} of 0.0006 (phase difference {circle around(1)}), 0.0013 (phase difference {circle around (2)}), 0.0017 (phasedifference {circle around (3)}) and 0.0024 (phase difference {circlearound (4)}).

Next, compensation of the oblique retardation achieved by using such aphase compensation film 45 having a negative dielectric anisotropy willbe explained.

FIG. 13A shows a refractive index ellipsoid of the phase compensationfilm 45 having a negative dielectric anisotropy in the verticaldirection of the substrate while FIG. 13B shows a refractive indexellipsoid of the liquid crystal layer 43 that has a positive dielectricanisotropy. Further, FIG. 14A shows a cross-section of the refractiveindex ellipsoid of FIG. 13A taken in the Y-Z plane, while FIG. 14B showsa cross-section of the refractive index ellipsoid of FIG. 13B taken inthe Y-Z plane. In the discussion hereinafter, it is assumed that thereis no in-plane anisotropy in any of the phase compensation film 45 andthe liquid crystal layer 43 (n_(x)=n_(y)).

Referring to FIGS. 13A and 13B and further with reference to FIGS. 14Aand 14B, it will be noted that the refractive indices of the ordinaryray and extraordinary ray of the light incident to an X-Y plane with anincident angle θ correspond to the major axis and the minor axis in thecase of the phase compensation film 45 and to the minor axis and themajor axis in the case of the liquid crystal layer 43, of an ellipsethat formed at the cross section of the refractive index ellipsoidsectioned by a plane

Referring to FIGS. 14A and 14B, the apparent refractive indices ny′ andnz′ respectively representing the refractive indices in the Y- andZ-directions for the case the incident light has impinged with an angleθ with respect to the normal direction of the substrate (Z-direction),are obtained according to the following equations.

${\frac{Y^{2}}{n_{y}^{2}} + \frac{Z^{2}}{n_{z}^{2}}} = 1$${\frac{n_{y}^{\prime 2}\cos^{2}\theta}{n_{y}^{2}} + \frac{n_{y}^{\prime 2}\sin^{2}\theta}{n_{z}^{2}}} = 1$$n_{y}^{\prime 2} = \frac{1}{\frac{\cos^{2}\theta}{n_{y}^{2}} + \frac{\sin^{2}\theta}{n_{z}^{2}}}$$\begin{matrix}{n_{y}^{2} = \frac{n_{y}n_{z}}{\sqrt{{n_{z}^{2}\cos^{2}\theta} + {n_{y}^{2}\sin^{2}\theta}}}} \\{= \frac{n_{z}}{\sqrt{{\frac{n_{z}^{2}}{n_{y}^{2}}\cos^{2}\theta} + \left( {1 - {\cos^{2}\theta}} \right)}}} \\{= \frac{n_{z}}{\sqrt{1 - {{\upsilon cos}^{2}\theta}}}}\end{matrix}$ wherein$\upsilon = {{{\frac{n_{y}^{2} - n_{z}^{2}}{n_{y}^{2}}.\frac{Y^{2}}{n_{y}^{2}}} + \frac{Z^{2}}{n_{z}^{2}}} = 1}$${\frac{n_{z}^{\prime 2}\sin^{2}\theta}{n_{y}^{2}} + \frac{n_{z}^{\prime 2}\cos^{2}\theta}{n_{z}^{2}}} = 1$$n_{z}^{\prime 2} = \frac{1}{\frac{\sin^{2}\theta}{n_{y}^{2}} + \frac{\cos^{2}\theta}{n_{z}^{2}}}$$\begin{matrix}{n_{z}^{2} = \frac{n_{y}n_{z}}{\sqrt{{n_{z}^{2}\sin^{2}\theta} + {n_{y}^{2}\cos^{2}\theta}}}} \\{= \frac{n_{z}}{\sqrt{{\frac{n_{z}^{2}}{n_{y}^{2}}\left( {1 - {\cos^{2}\theta}} \right)} + {\cos^{2}\theta}}}} \\{= {\frac{n_{z}}{\sqrt{\frac{n_{z}^{2}}{n_{y}^{2}} + {{\upsilon cos}^{2}\theta}}}.}}\end{matrix}$

The retardation values of the liquid crystal layer and the phasecompensation film and the values of the efficiency of compensationrepresented in Table 3 above were calculated based on the apparentrefractive indices n_(x)′, n_(y)′ and n_(z)′ as well as the incidentangle θ, and thus, incorporates the effect of oblique path of theincident light.

Referring to Table 3 again, it can be seen that the phase compensationfilms {circle around (1)} and {circle around (4)} cannot providesufficient compensation, while the phase compensation films {circlearound (1)} and {circle around (3)} can provide near 100% compensation.

It should be noted that such compensation of retardation changes withthe retardation dlc·Δn of the liquid crystal layer, and thus, theretardation compensation has to be changed when the retardation of theliquid crystal layer is changed.

Generally, the value of retardation is represented by the value in thedirection parallel to or perpendicular to the substrate. Thus, it ispreferable to represent the retardation of the phase compensation filmalso in terms of the value parallel to or perpendicular to thesubstrate, not by the value oblique to the substrate.

Thus, the preferable retardation value obtained as noted above isrepresented for the case of the reflector A having the averageinclination angle ζ of 13 degrees as0.5≦[df·{(n _(x) +n _(y))/2−n _(z)}]/(dlc·Δn)≦0.7.

Within this range, a conspicuous effect is achieved for the compensationof black representation mode, although there can be a case in which theretardation compensation deviates by about 10% from the optimum value.

In the case of using the reflectors B-D having the average inclinationangle ζ of 7-9 degrees, on the other hand, the liquid crystal layer 43has a retardation in the range of 11-16 nm in the non-activated state.In such a case, the phase compensation film {circle around (2)} providesthe best result. In this case, the preferable range of retardation ofthe phase compensation film is determined as0.4≦[df·{(n _(x) +n _(y))/2−n _(z)}]/(dlc·Δn)≦0.6,including the allowable margin from the optimum value.

Summarizing the foregoing results, it is concluded that the preferableretardation range of the phase compensation film 45 for thereflection-type liquid crystal display device 40 is determined in therange of0.4≦[df·{(n _(x) +n _(y))/2−n _(z)}]/(dlc·Δn)≦0.7.

When the inclination angle ζ has decreased below about 7 degrees, theincident angle θ1 for incorporating the environmental light becomes toosmall and it becomes difficult to incorporate the environmental light.

In the construction of FIG. 11, it is particularly advantageous to use aTAC film having a retardation of about 10 nm in the in-plane directionand about 50 nm in the normal direction for the phase compensation film45. With this, substantially ideal black mode compensation is achievedwith low cost.

It should be noted that the polarizer 47 generally has amoisture-blocking film of TAC but such a TAC film is disposed betweenthe ¼ wavelength film 46 and the polarizer 47. Thus, no compensationeffect comparable to the one achieved by the phase compensation film 45can be obtained by such a moisture resistance film. This point will benoted later.

In the liquid crystal display device 40 of FIG. 11, the ¼ wavelengthfilm 45 is disposed between the phase compensation film 45 and thepolarizer 47, wherein such a ¼-wavelength film shows smaller wavelengthdispersion as compared with the liquid crystal layer 43.

Thus, by disposing such a phase compensation film of small wavelengthdispersion between the polarizer 47 and the liquid crystal layer 43 andby achieving a 90-degree rotation of the polarization plane, it ispossible to realize excellent black mode representation characterized bysmall wavelength dispersion and hence small leakage of visible light.

By doing so, it is not preferable to dispose the ¼-wavelength film 46,in other words, a second phase compensation film, outside the phasecompensation film 45 or a first phase compensation film. It should benoted that the refractive index ellipsoid of the phase compensation film45 has an azimuth dependence, and the construction that disposes the¼-wavelength film 46 between the phase compensation film 45 and theliquid crystal layer 43 would results in a situation in which thelinearly polarized light passed through the polarizer is compensated. Inthis case, there can be a problem that a satisfactory compensation isachieved in a specific azimuth angle while no such a satisfactorycompensation is achieved in other azimuth angle. Thereby, the overallcompensation effect is reduced.

In the case the ¼-wavelength film 46 is formed outside the phasecompensation film 45, the phase compensation film 45 compensates for theoptical phase of the circularly polarized light passed through the¼-wavelength film 46, and the effect of the azimuth dependence iseliminated. It should be noted that circularly polarized light isequivalent in all the azimuth directions, and thus, the opticalcompensation is achieved for all the azimuth directions in this case,even when there is an azimuth dependence on the refractive indexellipsoid of the phase compensation film 45.

Meanwhile, a phase compensation film such as a TAC film 45 has anin-plane retardation axis. Thus, there is caused a problem in that theretardation of the ¼-wavelength film 46 is affected when such a TAC film45 is laminated with the ¼-wavelength film 46. In the case the¼-wavelength film 46 and the phase compensation film 45 are laminated inthe state that respective retardation axes coincide each other, forexample, the retardation value of such a laminated structure in thein-plane direction becomes the sum of the retardation values of thephase compensation film 45 and the ¼-wavelength film 46. In the casethey are disposed such that respective retardation axes cross with eachother perpendicularly, the retardation becomes the difference betweenthe retardation values of the phase compensation film 45 and the¼-wavelength film 46.

Thus, in the case an element formed of lamination of a ½-wavelength filmand a ¼-wavelength film is used for the ¼-wavelength film 46 forminimizing the wavelength dispersion, there arises a problem that thephase compensation film 45 is included in the laminated structure in thecase the in-plane retardation axis of the phase compensation film 45 isoffset from the in-plane retardation axis of the ¼-wavelength film 46.Thereby, there can be a possibility that the wavelength dispersioncharacteristic is affected.

In order to avoid this problem, it is preferable to coincide thein-plane retardation axis of the TAC film forming the phase compensationfilm 45 with the in-plane retardation axis of the ½-wavelength film or¼-wavelength film constituting the laminated ¼-wavelength film 46. Inthis case, there is caused no effect other than increase or decrease ofthe retardation.

Particularly, it is possible to achieve complete compensation of theblack representation by disposing the phase compensation film 45 and the¼ wavelength film 46 in such a relationship that respective in-planeretardation axes extend parallel with each other and that the sum of thein-plane retardation becomes almost ¼ of the visible wavelength. Bydoing so, it is possible to suppress the deviation of retardation of the¼-wavelength film 46 caused by the in-plane retardation of the¼-wavelength film 46.

Especially, in the case the ¼-wavelength film 46 is an element oflaminated structure as noted before, it is sufficient to align thein-plane retardation axis of the phase compensation film 45 with thein-plane retardation axis of any of the ¼ wavelength film or the ½wavelength film. Further, adjustment of retardation is conducted suchthat the sum of the in-plane retardation of the ¼-wavelength film andthe phase compensation film 45 becomes equal to ¼ wavelength or suchthat the sum of the in-plane retardation of the ½-wavelength film andthe phase compensation film 45 becomes equal to ½ wavelength. In thiscase, it is not always true that the sum of the in-plane retardation ofthe phase compensation film 45 and the laminated ¼-wavelength film 46becomes equal to ¼ of the visible wavelength. However, a similar effectis achieved when the retardation of one of the phase compensation filmsin the laminated ¼-wavelength film 46 is adjusted such that thelaminated ¼-wavelength film 46 as a whole provides the in-planeretardation equal to ¼ of the visible wavelength.

Next, the fabrication process of the reflection-type liquid crystaldisplay 40 of FIG. 11 will be explained.

In the present embodiment, a resist film is applied on the TFT substrate41 by a spin coating process with a thickness of about 1 μm and aprebaking process is conducted at 90° C. for 30 minutes. Thereafter, theresist film thus formed is exposed to ultraviolet radiation while usinga mask corresponding to the projection and depression pattern. Bydeveloping the resist film after exposure, followed by a baking processat 135° C. for 40 minutes and a final baking process at 200° C. for 60minutes, the projection and depression pattern 42 is formed with theaverage inclination angle <ζ> of 7.7 degrees. It should be noted thatthis inclination angle is changed arbitrarily by changing the bakingtemperature and the baking time.

Further, an Al film 42A is deposited on the surface of the projectionand depression pattern 42 thus formed by an evaporation depositionprocess with a thickness of 200 nm.

Further, the vertical alignment molecular orientation films 42C and 42Dare applied to the TFT substrate 41 thus processed and also to theopposing substrate 44, and the substrates 41 and 44 thus processed areassembled together via intervening spacers each having a diameter of 3μm, and a vacant panel is obtained.

Next, a liquid crystal having a negative dielectric anisotropy (Δ∈=−3.5)and a refractive index difference Δn of 0.067 between the extraordinaryray and the ordinary ray is injected into the gap formed between theforegoing substrates 41 and 42. With this, a liquid crystal panel isobtained.

Next, two biaxial TAC films having an in-plane retardation of 10 nm anda normal direction retardation of 47 nm are laminated on the substrate44 as the phase compensation film 45 such that the in-plane retardationaxis has an azimuth angle of 85 degrees, and a ¼-wavelength film havingan in-plane retardation of 135 nm and a ½-wavelength film having anin-plane retardation of 250 nm are laminated consecutively with theazimuth angle of the retardation axes set to 140 degrees and 85 degrees,respectively. Thereby, the laminated ¼-wavelength film 46 is formed.Further, the polarizer 47 is formed on the ¼-wavelength film 46 suchthat the absorption axis is oriented in the azimuth direction of 75degrees.

In the VA-mode reflection-type liquid crystal display device 40 thusformed, it is possible to suppress the wavelength dispersion by usingthe laminated ¼-wavelength film as the ¼-wavelength film 46. Further, bysetting the direction of the in-plane retardation axis of the phasecompensation film 45 to be coincident to the in-plane retardation axisof the ½-wavelength film constituting the laminated ¼-wavelength film46, the value of the in-plane retardation of the ½-wavelength film isreduced by the amount of the in-plane retardation of the phasecompensation film 45, and the ¼-wavelength film 46 as a whole shows anin-plane retardation value corresponding to ½ wavelength at the greenwavelength (540 nm), in which the sensitivity of human eye is largest.

On the other hand, the phase compensation film 45 is a film having anegative dielectric anisotropy for compensating for the retardation ofthe liquid crystal layer in the state the electric field is applied,wherein the phase compensation film 45 has an in-plane retardationdf·{(n_(x)+n_(y))/2−n_(z)} satisfying the relationship ofdf{(n _(x) +n _(y))/2−n _(z)}/(dlc·Δn)=0.47with respect to the in-plane retardation dlc·Δn of the liquid crystallayer 43.

Table 4 below shows the result of measurement of reflectivity of thereflection-type liquid crystal display device 40 thus obtained for eachof the white representation mode and black representation mode byapplying a predetermined drive voltage. The measurement of Table 4 wasmade by using a spectrometer that uses an integrating sphere opticalsource (Embodiment 4). It should be noted that an integrating sphereoptical source is a diffusive optical source emitting light in allangles and all the azimuth directions and can provide illumination closeto the environmental light such as interior lighting or sunlight.

TABLE 4 reflectivity orientation black white contrast Embodiment 4 VA0.53 12.64 24.1 Comparative4 VA 0.68 12.66 18.6 Comparative5 VA 0.6612.55 18.9 Comparative6 VA 0.71 12.74 18.1 Comparative7 horizontal 0.7112.86 18.0

Referring to Table 4, it can be seen that the reflection-type liquidcrystal display device 40 of the present embodiment can achieve thereflectivity of 0.53 at the black representation mode and thereflectivity of 12.64 in the white representation mode. With this, acontrast ratio of 24.1 is realized.

In Table 4, the results of comparative experiments 4-7 (Comparative4-Comparative 7) are also listed.

In the comparative experiment 4, the order to the phase compensationfilm 45 and the laminated ¼-wavelength film 46 is reversed, and thus,the substrate 44 is first covered with the ¼-wavelength film of thelaminated ¼-wavelength film 46, next with the ½-wavelength film of thelaminated ¼-wavelength film 46, and finally the phase retardation film45 on the foregoing ½-wavelength film. Otherwise, the construction ofthe liquid crystal display device of the comparative experiment 4 isidentical with the one used in Embodiment 4.

In the comparative experiment 5, on the other hand, a liquid crystaldisplay device similar to the one used in Embodiment 4 is used exceptthat the ½-wavelength film constituting the upper layer of the laminated¼-wavelength film 46 is replaced with a uniaxial film having an in-planeretardation of 270 nm. Further, the ¼-wavelength film in the laminated¼-wavelength film 46 is disposed such that the retardation axis op the¼-wavelength film is coincident to the anchoring orientation (rubbingorientation) of the liquid crystal layer. With this, the in-planeretardation is reduced by 20 nm as compared with the ¼-wavelength filmof Embodiment 4.

In the comparative experiment 6, on the other hand, the phasecompensation film 45 of the liquid crystal display device of Embodiment4 is eliminated Further, an uniaxial film having an in-plane retardationof 270 nm is used for the ½ wavelength film constituting a part of thelaminated ¼-wavelength film.

In the comparative experiment 7, on the other hand, a horizontalalignment film is applied to the substrates 41 and 44, and thesubstrates 41 and 44 are assembled with each other via spacers having adiameter of 3 μm. Further, a liquid crystal having a positive dielectricanisotropy (Δ∈=6.0) and a refractive index difference Δn between theextraordinary ray and the ordinary ray of 0.067 is confined in the gapformed between the substrates 41 and 44. Thus, the liquid crystaldisplay device of the comparative experiment is a reflection-type liquidcrystal display device of TN-mode.

Referring to Table 4 again, it will be noted that the liquid crystaldisplay device of the present embodiment provides a reflectivity lowerthan any other liquid crystal display devices of the comparativeexperiments in the black representation mode, and as a result, a highestcontrast ratio is achieved by the liquid crystal display device ofEmbodiment 4.

FIGS. 15 and 16 show the reflectivity and contrast ratio of the blackrepresentation mode for the VA-mode reflection-type liquid crystaldisplay device 40 according to the present embodiment (Embodiment 4) forthe case the liquid crystal display device 40 is illuminated with a spotlight source with an incident angle of 25 degrees, wherein FIG. 15 showsthe reflectivity while FIG. 16 shows the contrast ratio. Further, FIGS.15 and 16 show the result of similar measurement with regard to theapparatus of the comparative experiment 6.

Referring to FIGS. 15 and 16, it can be seen that the black modereflectivity is reduced in the reflection-type liquid crystal displaydevice 40 of the present embodiment over the liquid crystal displaydevice of the comparative experiment for the entire azimuth angles andimprovement of contrast ratio is achieved.

Generally, there is a tendency that the reflectivity in the blackrepresentation mode becomes minimum in the reflection-type liquidcrystal display device having a single polarizer in the azimuthdirection corresponding to the absorption axis of the polarizer andmaximum in the azimuth direction corresponding to the transmission axis.

In FIGS. 15 and 16, too, it can be seen that the reflectivity in theblack representation mode takes a minimum value at the azimuth anglenear 255 degrees corresponding to the absorption axis of the polarizer47 and that a maximum contrast ratio is achieved in this azimuth angle.

Table 5 below shows the reflectivity of the black representation modeand white representation mode as well as the azimuth dependence of thecontrast ratio for the liquid crystal display device 40 of Embodiment 4in the direction of the absorption axis of the polarizer in comparisonwith the liquid crystal display device of the comparative experiment 6.

TABLE 5 reflectivity mode black white contrast Embodiment 4 VA 0.3624.10 67.5 Comparative6 VA 0.44 21.47 48.7

Referring to Table 5, it can be seen that the reflectivity of the blackrepresentation mode is reduced by 18% in the present embodiment ascompared with the comparative experiment in the azimuth angle of about255 degrees corresponding to the direction of the absorption axis of thepolarizer. Further, Table 5 indicates that the contrast ratio hasincreased in this azimuth angle from 48.7% to 67.5%.

Fifth Embodiment

Next, description will be made on a reflection-transmission-type liquidcrystal display device according to a fifth embodiment of the presentinvention.

FIG. 17 shows the general construction of a conventionalreflection-transmission-type liquid crystal display device.

Referring to FIG. 17, the reflection-transmission-type liquid crystaldisplay device 50 is basically formed of a pair of glass substrates 51and 52 and a liquid crystal layer 53 confined therebetween, wherein atransparent electrode 52A is formed on the inner surface of the glasssubstrate 52 uniformly. On the other hand, there is formed aplanarization film 51A on the inner surface of the glass substrate 51and an opening 51 a is formed in the planarization film 51A as anoptical transmission window.

On the surface of the planarization film 51A, there is formed areflection electrode 51B having projections and depressions, and atransparent electrode 51C is formed on the substrate 51 incorrespondence to the foregoing opening 51 a.

Further, there is formed a circular polarizer 54 on the outer side ofthe substrate 51 and another circular polarizer 55 is formed on theouter side of the substrate 52.

In the reflection-transmission type liquid crystal display device 50, inwhich optical switching is achieved by modulating the retardation of theliquid crystal layer 53, it is necessary to set the optical path lengthof the light in the liquid crystal layer 53 incident thereto through theglass substrate 52 and exit therefrom after being reflected by thereflection electrode 51B to be equal to the optical path length of thelight that enters the liquid crystal layer 53 from the substrate 51through the optical window 51 a and exits after passing through theliquid crystal layer 53 and the glass substrate 52. This means that itis necessary to form the planarization film 51A to have a thickness of ½the thickness of the liquid crystal layer 53.

However, fabrication of such a liquid crystal display device is complexin view of the need of the steps of forming the thick planarization film51A on the substrate 51, forming the reflection electrode 51B on theplanarization film 51A, forming the optical window 51 a and forming atransparent electrode 51C on the substrate 51 in correspondence to theoptical window 51 a, in addition to ordinary manufacturing steps forfabricating a liquid crystal display device. Thus, the liquid crystaldisplay device 50 of the conventional reflection-transmission-typesuffers from the problem of increased cost.

Further, in the reflection-transmission-type liquid crystal displaydevice 50 of FIG. 17, there arises the need of forming a barrier metalfilm 51 b at the interface between the Al reflection electrode 51B andthe transparent electrode 51C of ITO for preventing corrosion caused byelectrolytic effect.

FIG. 18, on the other hand, shows the construction of areflection-transmission-type liquid crystal display device 60 accordingto a fifth embodiment of the present invention that eliminates theforegoing problems.

Referring to FIG. 18, the liquid crystal display device 60 is basicallyformed of a pair of glass substrates 61 and 62 and a polymer networkliquid crystal layer 63 confined therebetween, wherein a transparentelectrode 62A is formed uniformly on the inner surface of the glasssubstrate 62.

On the inner surface of the glass substrate 61, there is formed areflection electrode pattern 61A having a slit-shape opening 61 a, andthe liquid crystal layer 63 takes an optically transparent state in thenon-activated state of the liquid crystal display device in which nodrive voltage is applied to the liquid crystal layer 63. In theactivated state in which a driving electric field is applied to theliquid crystal layer 63, on the other hand, the liquid crystal layer 63takes a scattering state. Such a liquid crystal layer 63 may be realizedy using a polymer network liquid crystal disclosed for example in theJapanese Laid-Open Patent Publication 5-27228.

Further, a circular polarizer 64 is provided on the outer side of theglass substrate 61 and a linear polarizer 65 is provided on the outerside of the glass substrate 62.

FIGS. 19A and 19B are diagrams explaining the operation of thereflection-transmission-type liquid crystal display device 60 of FIG. 18in the black representation mode and white representation mode,respectively.

Referring to FIG. 19A, the left side of the drawing shows thereflection-mode operation while the right side shows thetransmission-mode operation, wherein it will be noted that the incidentlight from the front side of the liquid crystal panel is converted intolinearly polarized light in the reflection mode operation by the linearpolarizer 65 and is converted further into circularly polarized light bythe liquid crystal layer 63 of non-scattering state. It should be notedthat the liquid crystal layer 63 has a retardation of about ¼ wavelengthof the incident light and has a retardation axis forming an angle of 45degrees with respect to the absorption axis of the polarizer 65. Here,it should be noted that the retardation of the liquid crystal layer 63in the non-scattering state is by no means limited to ¼ of the incidentlight wavelength λ or visible wavelength but may have the value of(0.5n+¼)λ; n=0, 1, 2. . . n, wherein n is a natural number.

The incident light thus converted to circularly polarized light is thenreflected by the reflection electrode 61A in the state of the circularlypolarized light and is converted to linear polarized light having apolarization plane crossing the initial polarization planeperpendicularly. The reflected light having such a linearly polarizedstate and exiting the liquid crystal layer 63 is then cut off by thelinear polarizer 65, and the desired black representation is obtained.

In the transmission-mode operation, the incident light incident to thesubstrate 61 from the backside of the liquid crystal panel is convertedcircularly polarized light upon passage through the circular polarizer64 and is introduced into the liquid crystal layer 63 through theoptical window 61 a in the reflection electrode 61A.

As the liquid crystal layer 63 is in the non-scattering state, theincoming circularly polarized light is converted to linearly polarizedlight having a polarization plane crossing the absorption axis of thelinear polarizer 65 upon passage through the liquid crystal layer 63similarly to the case of the reflected circularly polarized lightexplained above, and the transmission light passed through the liquidcrystal layer 63 is cut off also by the linear polarizer 65.

In the white representation mode of FIG. 19B, on the other hand, theliquid crystal layer 63 is in the scattering state and the linearlypolarized light passed though the linear polarizer 65 and incident tothe liquid crystal layer 63 is scattered and the scattered light isreflected by the reflection electrode 61A. It should be noted that suchscattered light undergoes further scattering upon passage through theliquid crystal layer 63 in the reverse direction after reflection, andas a result, the linear polarizer 65 receives the light includingtherein various polarization components of various polarization planesin addition to the polarization component having a polarization planeparallel to the absorption axis thereof.

Thus, the polarization component having a polarization plane crossingthe absorption axis passes through the polarizer 65 in the form oflinearly polarized light, and a desired white representation isobtained.

The same explanation applied also to the case of the transmission light.Thus, the incident light incident to the substrate 61 through thecircularly polarized light is scattered at the liquid crystal layer 63,and those polarization components formed as a result of the scatteringand having a polarization plane crossing the absorption axis of thepolarizer 65 passes through the polarizer 65.

In the reflection-transmission-type liquid crystal display device ofsuch a construction, there is no need of forming the thick planarizationfilm 51A or electrode 51B carrying a scattering structure, or atransparent electrode 51C corresponding to the optical window 51 a. Itis sufficient to merely form the reflection electrode 61A patterned toform a slit on the inner surface of the substrate 61. Further, it shouldbe noted that the reflection electrode 61A does not make a contact withthe transparent electrode, and thus, there is no need of forming abarrier metal layer.

Thus, the fabrication process of the liquid crystal display device ofthe present embodiment is easy to produce and the fabrication cost isreduced significantly.

Further, it should be noted that the liquid crystal display device thatuses the transition of state of the liquid crystal layer between thenon-scattering state and scattering state has no problem of limitedviewing angle, and excellent viewing angle characteristics can beachieved.

In the example of FIG. 18, it should be noted that the liquid crystallayer has a retardation value of ¼ wavelength of the incident light inthe non-scattering state. On the other hand, it is also possible to usea liquid crystal layer having a very small retardation as represented inFIG. 20, wherein it should be noted that FIG. 20 shows a liquid crystaldisplay device 70 according to a modification of the present embodiment.In FIG. 20, those parts corresponding to the parts described previouslyare designated by the same reference numerals and the descriptionthereof will be omitted.

Referring to FIG. 20, a polymer dispersion liquid crystal layer 73having a very small in-plane retardation in the non-scattering state isused in the reflection-type liquid crystal display device 70 in place ofthe liquid crystal layer 63. The liquid crystal layer 73 has an in-planeretardation smaller than the product Δn·d of the liquid crystal used forthe scattering layer wherein Δn represents the birefringence and drepresents the cell thickness. It is thereby preferable to set thein-plane retardation negligible in the liquid crystal layer 73.Associated with this, the linearly polarized light is replaced by acircular polarizer 66.

FIGS. 21A and 21B show the operation of the reflection-transmission-typeliquid crystal display device 70 of FIG. 20 respectively in the blackrepresentation mode and white representation mode.

Referring to FIG. 21A, the left side of the drawing shows the reflectionmode operation it the black representation mode, while the right drawingshows the transmission mode operation. Thus, in the reflection mode, theincoming light from the front side of the liquid crystal panel isconverted to circularly polarized light by the circular polarizer 66,wherein the circularly polarized light thus formed passes through theliquid crystal layer 73 in the state of the circularly polarized lightin view of the ignorable small retardation of the liquid crystal layer.The liquid crystal layer is in the non-scattering state.

The incident light thus passed through the liquid crystal layer 73 isreflected by the reflection electrode 61A in the circularly polarizedstate and passes through the liquid crystal layer 73 in the reversedirection while maintaining the circularly polarized state. Thecircularly polarized light thus passed through the liquid crystal layer73 enters into the circular polarizer 66 in the reverse direction and iscut off.

In the transmission mode operation, on the other hand, the incominglight incident to the substrate 61 from the backside is converted tocircularly polarized light by the circular polarizer 64 and isintroduced into the liquid crystal layer 73 through the optical window61 a in the reflection electrode 61A.

As the liquid crystal layer 73 is in the non-scattering state, theincident circularly polarized light passes through the liquid crystallayer 73 while maintaining the circularly polarized state and is cut offby the circular polarizer 66 similarly to the reflected circularlypolarized light explained above.

In the white representation state of FIG. 19B, the liquid crystal layer73 is in the scattering state, and thus, the circularly polarized lightincident to the liquid crystal layer 73 experiences scattering in theliquid crystal layer 73. The scattered incident light is then reflectedby the reflection electrode 61A and experiences further scattering as itis propagated through the liquid crystal layer 73 in the reversedirection. As a result, the circular polarizer 66 at the front sidereceives various polarization components having various polarizationplanes.

Thus, the component having a polarization plane perpendicular to theabsorption axis passes through the polarizer 66 and the desired whiterepresentation is achieved.

The same situation hold true also in the case of the transmission lightin that the incoming light incident to the substrate 61 from thebackside through the circular polarized light 64 is scattered in theliquid crystal layer 73, and the polarization component formed as aresult of the scattering and having a polarization plane crossing theabsorption axis of the polarizer 66 passes through the polarizer 66.

In the reflection-transmission-type liquid crystal display device 70 ofsuch a construction, there is no need of forming the thick planarizationfilm 51A or electrode 51B carrying a scattering structure thereon, or atransparent electrode 51C corresponding to the optical window 51 a,contrary to the conventional reflection-transmission-type liquid crystaldisplay device 70, and it is sufficient to form the reflection electrode61A patterned according to the slit shape on the inner surface of thesubstrate 61. Further, it will be noted that the reflection electrode61A does not make a contact with the transparent electrode, and thus,there is no need of forming a barrier metal layer. Thus, the fabricationprocess is simplified and the cost of the liquid crystal display deviceis reduced significantly.

In such a liquid crystal display device that uses transition of state ofthe liquid crystal layer between the non-scattering state and thescattering state, there arises no problem of limited viewing angle, andexcellent viewing angle characteristics can be achieved.

Table 6 below compares the fabrication process of the conventionalreflection-transmission-type liquid crystal display device 50 of FIG. 17and the reflection-transmission-type liquid crystal display device 70 or70 of the present invention.

TABLE 6 Conventional Present invention planarization necessary notnecessary film surface necessary not necessary scattering structuretransparent necessary not necessary electrode reflection necessarynecessary electrode

Referring to Table 6, it will be noted that the present invention caneliminate the step of forming the planarization film 51A, the step offorming the projection and depression pattern 51B on the planarizationfilm 51A and further the step of forming the transparent electrode 51Con the optical window.

Thus, in the present invention, it is sufficient to merely pattern thereflection electrode and the fabrication process of thereflection-transmission-type liquid crystal display device is simplifiedsubstantially.

Meanwhile, in the reflection-transmission-type liquid crystal displaydevice 60 of FIG. 18 or in the in the reflection-transmission-typeliquid crystal display device 70 of FIG. 20, in which a uniformelectrode is formed on a front substrate and a slit-shape electrodepattern is formed on the rear substrate, there are several possibledriving modes for applying a driving electric field to the liquidcrystal layer 63 as represented in FIGS. 22-24.

FIG. 22 is a so-called lateral electric field mode or IPS mode and adrive voltage is applied across a pair of mutually adjacent electrodefingers of the interdigital electrode constituting the reflectionelectrode.

FIG. 23, on the other hand, shows a driving mode designated herein asvertical electric field mode or S mode for distinction from the IPSmode, wherein a drive electric voltage is applied between the opposingelectric field 62 and the reflection electric field 61A.

Further, FIG. 24 shows a driving mode designated hereinafter as one-sidevertical electric field mode or sS mode in which the IPS mode and the Smode noted above are combined. Thus, in the driving mode of FIG. 24, theopposing electrode 62 and one of the electrode fingers are driven to afirst voltage level and the electrode fingers at both sides are drivento a second drive voltage.

FIG. 25A shows an example of the construction of the reflectionelectrode 61A used in the S driving mode of FIG. 23, while FIG. 25Bshows the construction of the reflection electrode 61A used in the IPSdriving mode of FIG. 22 or sS driving mode of FIG. 24.

Referring to FIG. 25A, there is formed a TFT 61T, a gate electrode 61Gand a data electrode 61D on the glass substrate 61, and an electrodehaving a slit in corresponding to the transmission region 61 a is formedas the reflection electrode 61A.

In the construction of FIG. 25B, on the other hand, pluralityinterdigital electrodes 61A₁ and 61A₂ are formed on the glass substrate61 alternately in addition to the TFT 61T, gate electrode 61G and thedata electrode 61D, wherein the interdigital electrode 61A2 is connectedto a common line 61C. Further, there is formed a gap between theelectrode 61A₁ and the electrode 61A₂ in correspondence to thetransmission region 61 a.

By using the TFT substrate of FIG. 25A or FIG. 25B for the substrate 61and assembling the substrates 61 and 62 together via a spacer having adiameter of 5 μm, liquid crystal display devices having the constructionof the liquid crystal display device 60 of FIG. 18 have beenmanufactured respectively for testing the IPS driving mode, S drivingmode and the, sS driving mode. Thereby, a horizontal alignment film isformed on each of the substrates 61 and 62, and the alignment film issubjected to a rubbing process such that the liquid crystal moleculescause a homogeneous alignment in the direction perpendicular to the slitdirection.

Further, a liquid crystal mixture of a UV-curable liquid crystal and aliquid crystal having a birefringence Δn of 0.2306 and a dielectricanisotropy Δ∈ of 15.1 is confined into the gap formed between thesubstrates 61 and 62. Further, by conducting ultraviolet irradiation, apolymer network scattering layer is formed in the liquid crystal layer63.

FIG. 26 shows the relationship between the applied drive voltage and thetransmittance for the reflection-transmission-type liquid crystaldisplay device 60 thus formed for the case the width E of the electrodepattern 61A is set to 4 μm and the width G of the slit 61 a is changedvariously. In FIG. 26, it should be noted that the electrode width E andthe slit width G are represented in terms of microns. Further, thetransmittance is normalized by the transmittance in the non-activatedstate.

Referring to FIG. 26, it will be noted that the drive voltage is reducedwith reducing slit width G and that a minimum drive voltage is achievedin the case of using the S driving mode.

In another experiment of the present embodiment, a liquid crystaldisplay device having the construction of FIG. 18 is formed by using theTFT substrate of the construction shown in FIG. 25A or 25B.

In this experiment, a horizontal alignment film is formed on the surfaceof the substrate 61 or opposing substrate 62 by a PVA film or a solublepolyimide film. After applying a rubbing process to the alignment filmfor causing a homogenous alignment in the liquid crystal molecules, thesubstrates 61 and 62 are assembled together with intervening spacerseach having a diameter of 2.3 μm, and a liquid crystal mixturecontaining a nematic liquid crystal having a birefringence Δn of 0.067added with a UV-curable liquid crystal containing a polymerizationstarter with a proportion of 10 weight % is introduced into the gapformed between the substrates 61 and 62.

Further, by applying ultraviolet radiation to the liquid crystal panelthus formed, there is formed a polymer network liquid crystal having aretardation of 154 nm.

Further, a linear polarizer 65 is provided on the outer side of thesubstrate 62 such that the transmission axis of the polarizer 65 isoriented with an angle of about 45 degrees from the direction ofalignment of the liquid crystals. Further, a circular polarizer 64 isprovided at the outer side of the substrate 61.

Thus, it becomes possible to produce the reflection-transmission-typeliquid crystal display device 60 with low cost.

In another experiment, the reflection-transmission-type liquid crystaldisplay device 70 of FIG. 20 is manufactured by using a TFT substratehaving a construction of FIG. 25A or 25B for the TFT substrate 61.

In this experiment, the substrate 61 and the opposing substrate 62 areassembled together via intervening spacers having a diameter of 6 μm,and a liquid crystal mixture containing a liquid crystal having abirefringence Δn of 0.23 added with a UV-curable resin monomer with aproportion of 20 weight %, is introduced into the gap formed between thesubstrates 61 and 62. By applying ultraviolet irradiation to the liquidcrystal layer thus formed, the polymer-dispersed liquid crystal layer 73is obtained.

By providing the circular polarizers 64 and 66 at respective outer sidesof the TFT substrate 61 and the opposing substrate 62, thereflection-transmission-type liquid crystal display device 70 thatprovides the white representation mode in the non-activated state whereno drive voltage is applied and the black representation mode in theactivated state, is obtained.

In a further experiment, the reflection-transmission-type liquid crystaldisplay device 70 of FIG. 20 is formed by using a TFT substrate of theconstruction shown in FIG. 25A or 25B for the substrate 61.

In this experiment, a vertical alignment film of PVA or solublepolyimide is formed on the surface of the substrates 61 and 62, and thesubstrates 61 and 62 are assembled together via spacers having adiameter of 5 μm. Further, a liquid crystal mixture containing a liquidcrystal having a birefringence Δn of 0.23 added with a UV-curable resincontaining a polymerization starter with a proportion of 10 weight % isintroduced into the gap formed between the substrates 61 and 62, and thepolymer network liquid crystal layer 73 is obtained by applyingultraviolet irradiation.

The reflection-transmission-type liquid crystal display device 70 isthen completed, by providing the circular polarizers 64 and 66 atrespective outer sides of the TFT substrate 61 and the opposingsubstrate 62, wherein the liquid crystal display device 70 thus formedprovides the black representation mode in the non-activated state inwhich no drive voltage is applied and the white representation mode inthe activated state.

FIG. 27 shows an example of providing a color filter CF to any of thereflection-transmission-type liquid crystal display device 60 of FIG. 18or the reflection-transmission-type liquid crystal display device 70 ofFIG. 20.

Referring to FIG. 27, it will be noted that the light incident throughthe substrate 62 from the front direction and reflected by thereflecting electrode 61A is passed through the color filter CF twice,while the light incident from the backside through the TFT substrate 61passes through the color filter CF only once.

Thus, in the case the color filter CF has a uniform color purity, therearises a problem in that the color purity of the reflected light and thecolor purity of the transmission light may be difference.

Thus, in the construction of FIG. 27, a part CF₁ of the color filter CFcorresponding to the transmission region 61 a is formed to have athickness twice as large as the remaining part of the color filter CFsuch that both the transmission light and the reflection light has thesame color purity.

FIG. 28 shows a modification of FIG. 27, wherein it will be noted thatthe color filter CF is formed on the substrate 61 and the thickness ofthe color filter CF is adjusted by using the reflection electrode 61F.

Thus, by forming the color filter CF on the substrate 61 with athickness twice as large as that of the reflection electrode 61A, itbecomes possible to set the thickness of the color filter CF for thepart located on the transmission region 61 a to be twice as large as thethickness of the color filter CF on the electrode 61A. In theconstruction of FIG. 29, such an adjustment of thickness of the colorfilter CF is achieved in a self-aligned manner, and there is no need ofany patterning process.

FIG. 29 shows a modification of FIG. 28 in which there is formed apattern 61B underneath the reflection electrode 61A by a resist film orthe like, in conformity with the reflection electrode 61A.

According to such a construction, the reflection electrode 61A is formedat an elevated position on the substrate 61 as compared with the case ofFIG. 28. It should be noted that the construction of FIG. 29 iseffective particularly when the thickness of the reflection electrode61A is small and coloring of the reflection light can be achievedsufficiently in the construction of FIG. 28.

Further, the present invention is not limited to the embodimentsexplained heretofore, but various variations and modifications may bemade without departing from the scope of the invention.

1. A reflection-type liquid crystal display device, comprising: a firstsubstrate; a second substrate disposed so as to face said firstsubstrate; a liquid crystal layer having a negative dielectricanisotropy disposed between said first and second substrates; and avertical alignment film formed on a surface of said first substrate anda surface of said second substrate, wherein said alignment film containsa vertical alignment component containing a side chain diamine with aproportion of 25% or more with regard to total diamine components.